Do We Know More About Electrical Stimulation

Than We Know About Pluto?

New Horizons for Electrical Stimulation?

by Karen Sheffler, MS, CCC-SLP, BCS-S of SwallowStudy.com

Introduction:

My son clutched his Pluto stuffed animal while we stayed up past his bedtime on July 14^th, following @NASANewHorizons on Twitter, to see if the mission had been successful. We have been fascinated by what used to be our 9^th planet. Pluto is a great example of how perspectives change as new information comes in. In 2006, scientists told the world that Pluto needed to be reclassified as a “dwarf” planet.

Similarly in the dysphagia world, new research in 2006 warned Speech-Language Pathologists that electrical stimulation may not always be safe and effective for our patients.

Now that we can finally begin writing the textbook on Pluto, hopefully, we can do the same for electrical stimulation. These next few years should bring more definitive information on the use of electrical stimulation for swallowing rehabilitation. Without this information, personal biases may rule.

What prompted me to write this blog?

I was asked an excellent question recently about why I did not yet have any information on my website about electrical stimulation for swallowing rehabilitation. I then asked myself: Why have I been hesitant to perform the modality of electrical stimulation in clinical practice?

I realize how much past experience can cloud or bias our ability to take in new research. I realized I needed to do more than give fly-by answers to the questions.

What is the latest research and expert opinion on this?

There have always been great individual stories of success, but would the person have made progress anyway regardless of the treatment modality?

As we know, anecdotal information and even evidence of a diet upgrade cannot be used as outcome measures. I recall Dr James Coyle, PhD, CCC-SLP, BCS-S making this point at the Dysphagia Research Society (DRS) Annual Meeting in March, 2015. A diet modification is a subjective measure, as there is too much influence from patient preference and clinician variability, as well as no diet and liquid standardization (See previous blog on diet standardization).

Where do I start?

I asked Dr. Ianessa Humbert PhD, CCC-SLP how she felt about the current state and future of electrical stimulation. Like the great teacher she is, she gave me homework!

She suggested her review article from 2012 and asked me to put together a review blog in anticipation of her Live Chat via NFOSD on July 27, 2015 (updated 2016).

1. Electrical Stimulation and Swallowing: How Much Do We Know? By Humbert, I.A., Michou, E., MacRae, P.R. & Crujido, L. (2012) Seminars in Speech and Language, 33 (3), 203-216. doi:  10.1055/s-0032-1320040 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3475497/
2. Free Live Chat with Dr Humbert: July 27, 8:00-9:30pm EST. Sorry this is over, but still submit questions/comments.
3. Dr Humbert also suggested to have people submit questions to my website. You can contact me privately using the Contact Me page, if you would like your questions to be anonymous. Otherwise, use comment section below.

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Of course, I’ve gotten carried away with my homework here. I cannot discuss this in 700 words! So to navigate this meaty blog on electrical stimulation, here are the sections:

1. My past exposure to electrical stimulation.
2. What further shaped my opinions and biases?
3. Do newer studies help clarify?
4. Some of the latest research on electrical stimulation presented at the Dysphagia Research Society Annual Meeting, March, 2015, Chicago, IL.

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First, my past exposure to electrical stimulation:

The issue of electrical stimulation (aka, “estim”) brought up lots of feelings and memories of previous talks I had seen by experts in the field: Jeri Logemann, PhD, CCC-SLP, BCS-S, Ianessa Humbert, PhD, CCC-SLP, and Susan Langmore, PhD, CCC-SLP, BCS-S.

Specifically, I recall sitting in a room at the Loews Hotel during the 2004 ASHA Convention in Philadelphia. (I have a good visual memory.) There, Dr Logemann discussed why the research at that time behind VitalStim (Freed, et al, 2001) did not support it’s ethical use in the clinic yet. Logemann encouraged our field to constantly critically analyze research. Wijting & Freed stated in the 2003 manual for VitalStim: “Most patients should demonstrate increased laryngeal elevation with stimulation during the first session, page 103.” However, independent research into VitalStim went on to disprove what the company claimed. Abrupt stimulation at maximum tolerance level can cause the larynx to descend and the laryngeal vestibule to open, potentially causing an increase in aspiration (See below regarding Humbert, et al., 2006; Ludlow, et al., 2007).

What else have I learned?

I found my huge handout from a 12 hour online course that I took in 2012, while racking up hours for my BCS-S. This course had been recorded in October of 2011 in Pittsburgh, PA. Dr Humbert had given a lecture on estim. Interestingly, the program labeled Dr Humbert’s session as: Electrical Stimulation: Finally, Something Good To Say About Using It! However, she titled her slides: Electrical Stimulation: What is it? When it works and when it doesn’t. Patient selection criteria. That has a different, more critical thinking feel, doesn’t it? See also Dr Humbert’s Critical Thinking in Dysphagia Management blog on DysphagiaCafe.com.

10 Tidbits I took away from that 2011 course:

1. FDA approval does not mean that it works, it just means that it does not kill them.
2. There is no needle or wire directed into a muscle of interest. The bipolar surface electrodes create an arc between 2 electrodes. This works well in physical therapy when applied to a big target muscle to augment purposeful movement. Most effective when placed over a “motor point,” where a nerve enters a muscle. Need to still have nerve attached and not severed.
3. When applied to the surface of the neck, the adipose tissue, the fascia, the platysma, and the extrinsic laryngeal muscles are the first to receive any current. The deep muscles get much weaker current.
4. Extrinsic laryngeal muscles are larger and get more stimulation.

• Suprahyoids (aka, submentals): mylohyoid, geniohyoid, anterior belly of the digastrics)
• Infrahyoids: sternothyroid, omohyoid, sternohyoid.
• See DysphagiaCafe.com for anatomy tutorials with two cadaver videos.

5. The golden nugget of the Thyrohyoid (intrinsic muslce to pull the larynx up and closed) is so deep that it does not receive stimulation. Per Humbert, Leelamanit, et al (2002) incorrectly concluded that the thyrohyoid muscle was being targeted and could lead to laryngeal elevation. Leelamanit’s conclusion was unfortunately reiterated by Park, et al (2009) in the introduction of the article.
6. If you stimulate the infrahyoids, you are pulling the larynx down. This could lead to aspiration if the patient is stimulated during the swallow.
7. If you stimulate only the suprahyoids/submentals, you may cause the hyoid to elevate. However, if hyoid pulls up, but the the deep thyrohyoid is weak and does nothing, then the laryngeal vestibule is yanked opened. This could potentially increase aspiration if the patient is stimulated during the swallow.
8. Humbert reviewed 13 studies, and she noted that 12 used functional outcome measures (i.e., diet, quality of life, length of stay), or bolus flow measures (i.e., aspiration). As she noted, bolus flow cannot be an outcome measure. We have to know what caused the bolus to flow that way. She stressed that studies need to use physiological measures to document change.
9. You really need to know exactly where the patient is weak and why before deciding on estim as a treatment plan.

• Humbert recommended to test the stimulation on a videoflouroscopy, to see if the patient can achieve enough elevation to overcome the descent.
• She speculated then that low levels of stimulation may contribute to sensory information and high motor levels could lead to resistance training effects.

10. Patient selection is crucial. It may be best utilized with upper motor neuron disorders, per Humbert. The peripheral nerves, as well as the motor neurons in the spine and brainstem, should be intact. It may be beneficial when the impairment is in the input from the cortex. The stimulation may foster neuroplasticity, as the cortex becomes more aware of the sensory input.

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What further shaped my opinions and biases?

1. Dr Humbert’s 2011 article:

Point/Counterpoint: Electrical Stimulation for Dysphagia: The Argument Against Electrical Stimulation for Dysphagia. Perspectives on Swallowing and Swallowing Disorders (Dysphagia). Link to pdf.

Here is the link for the paired article from Perspectives: The Argument For Electrical Stimulation.

2. My memory of a Boston-area Dysphagia Rounds years ago.

We had guest speakers and analyzed electrical stimulation. MGH Speech-Language Pathologists shared how they had experimented on themselves. They did simultaneous FEES and surface electrical stimulation to watch the intrinsic musculature. Even with the device turned up at maximum tolerance levels, they did not see any muscle activity/contractions intrinsically at rest. Dr Humbert recommended this link to Humbert, et al (2008), which objectively studying this issue. The guest speakers showed videoflouroscopic images of before and after estim treatment programs; however, the general consensus in the room was that the swallowing physiology did not improve significantly.

3. An article by Clark, et al (2009):

The authors performed a systematic review that concluded 10 of the 14 studies were exploratory and had significant methodological flaws. They noted that more high-quality studies are needed before firm conclusions can be made.

Clark, H., Lazarus, C., Arvedson, J., Schooling, T., & Frymark, T. (2009). Evidence-based systematic review: Effects of neuromuscular electrical stimulation on swallowing and neural activation. American Journal of Speech-Language Pathology, 18 (4), 361–375.

4. And more research…

Humbert, et al (2006) studied the immediate effects of surface electrical stimulation (SES) on hyo-laryngeal position at rest and during swallowing in healthy adults. They performed electrical stimulation with 10 electrode placements with simultaneous videoflouroscopy. They also looked at submental placement only (not proposed by Vital Stim). Placement below the hyoid bone caused laryngeal descent, but placement above the hyoid (submental only) did NOT cause a statistically significant change in elevation. It was a statistically significant finding that the person could not get the same elevation with the stimulation on, as without the stimulation. A normal subject had penetration to the level of the vocal cords with a stimulated swallow. Stimulated swallows were significantly less safe than non-stimulated swallows.

Ludlow, et al (2007) had similar methods, but tested chronically dysphagic adults (n=8 of those who could complete the study). In addition to stimulation at maximum tolerated levels, they were stimulated at low “sensory” stimulation levels. They also found the hyoid was pulled down by 5-10mm at rest when both submental and laryngeal electrode pairs stimulated at maximal tolerance levels. This downward pull of the hyoid is due to the sternohyoid being a larger muscle that overlies the deeper thyrohyoid. No significant laryngeal movement was noted with stimulation at rest. Even the submental placement of electrodes has difficulty reaching the deeper mylohyoid, which would pull the hyoid upward. They concluded that the stimulation was not deep enough to stimulate the thyrohyoid or mylohyoid muscles. They went on to test low “sensory” levels of stimulation and captured changes best with the NIH-SSS or Swallowing Safety Scale (rates abnormalities in pooling, lack of esophageal entry and penetration/aspiration). No statistically significant change noted in the Penetration-Aspiration Scale (PAS); however, 6 out of 8 people had improvements on the NIH-SSS. The authors speculated that maybe you could increase awareness of swallowing with this “sensory stimulation” during swallowing.

After Ludlow and team’s research, I wonder if people jumped on the idea to use estim in the clinic as a resistance exercise. This may have come from the unexpected relationship Ludlow, et al (2007) noted: When patients had the greatest hyoid descent at rest, they had the greatest improvement on the PAS. They speculated that when the patient felt a greater downward pull, he/she was stimulated to swallow with more effort to compensate. However, I wonder how they can make such a profound statement with only 8 patients for whom, “no group change in aspiration was noted on either scale with motor levels of stimulation (page 8).”

They did qualify the speculations with: “If a patient is unable to produce any hyolaryngeal elevation, and therefore, would not be able to resist the hyoid depression induced by stimulation, stimulation might put such a patient as greater risk of aspiration as the hyo-laryngeal complex is held down during swallowing.” (page 8)

This resistance training concept may have prompted Park, et al. (2009) to test the effects of electrical stimulation coupled with effortful swallowing. They also had small numbers, with 8 healthy young adults randomized to the experimental group and 8 to the control group. Only the infrahyoid area was targeted. No improvement was seen in forward movement of the hyoid. They noted that there was an increase in elevation of the hyoid immediately post exercise, but this was not maintained at the 2 week follow-up.

“Before such a tool is used in therapy, improved understanding of its immediate effects should be gained…before it is applied widely to a variety of patients regardless of their risk of aspiration with hyoid lowering (page 9),” Ludlow, et al (2007).

Have we made progress? Do we have a better understanding in 2015?

I am stuck somewhere between 2006 and 2011!

Anyone have a time-machine?

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Do newer studies on electrical stimulation help clarify?

In addition to the reviews above by Humbert (2011) and Humbert, et al (2012), I found this 2014 review by Poorjavad, et al. However, it continued to echo my concerns.

Poorjavad, M., et al. (2014). Surface electrical stimulation for treating swallowing disorders after stroke: A review of the stimulation intensity levels and the electrode placements. Stroke Research and Treatment, Vol 2014, 7 pages. https://www.hindawi.com/journals/srt/2014/918057/

Poorjavad and team stated:

“But, in spite of this increasing interest, there are important methodological issues about many of these existing publications that cause concerns regarding their therapeutic outcomes.” (quotations from 2^nd paragraph of introduction). The authors went on to say that while some studies have shown small improvements (Carnaby-Mann & Crary, 2007), others have shown the stimulated swallow to be less safe (Heck, et al., 2012). See some of their recommended references here:

1. Steele, C.M., Thrasher, A.T. & Popovic, M.R. (2007). Electric stimulation approaches to the restoration and rehabilitation of swallowing: a review. Neurological Research, 29 (1), 9–15. View at Google Scholar
2. Carnaby-Mann, G.D. & Crary, M.A. (2007). Examining the evidence on neuromuscular electrical stimulation for swallowing: a meta-analysis. Archives of Otolaryngology: Head and Neck Surgery, 133 (6), 564–571. View at Google Scholar
3. Steele, C.M. (2004). Electrical stimulation of the pharyngeal swallow: does the evidence support application in clinical practice? Journal of Speech-Language Pathology and Audiology, 28, 78–84. View at Google Scholar
4. Heck, F.M., Doeltgen, S.H. & Huckabee, M.L. (2012). Effects of submental neuromuscular electrical stimulation on pharyngeal pressure generation. Archives of Physical Medicine and Rehabilitation, 93, (11), 2000–2007. View at Google Scholar 

I reviewed two more studies from Park, et al (2012) and Sun, et al (2013). However, I was frustrated by some methodological issues.

1. Park, et al (2012) returns with another study on effortful swallow training with electrical stimulation in stroke patients. Effortful swallow was only instructed as: “push really hard with your tongue.” Thirty patients with post-stroke dysphagia were eligible. Dysphagia was confirmed by videoflouroscopy as “any abnormality found in the VFSS.” 10 patients were excluded due to the inability to “overcome stimulation” and elevate the larynx. This shows us the need to check with videoflouroscopy first before enrolling a patient in estim.

Another issue was that the patients were only >1month post-stroke, and there was no chart of the subjects to learn more details. The number of subjects dropped again to 18, as one patient could not continue due to intolerable pain and another was transferred to another hospital. Are these all fairly acute inpatient stroke patients? Nine subjects were in the experimental group with stimulation at 7.33mA +/- 1.12 and 9 in the control group, receiving “placebo” stimulation at 2.89mA +/- 1.05. This “placebo” was actually at a “sensory” stimulation level, with a stimulation intensity at the level of just feeling a tingling sensation. They completed 3 sessions of 20 minutes of exercise per week for 4 weeks. A session consisted of two 10-minute exercises, where they were asked to forcefully swallow every 10 seconds during stimulation. It appears that the biomechanical measurements analyzed on video were taken NOT in the presence of stimulation during the swallow. The authors report they evaluated the immediate training effect. No long-term effects were measured as in Park, et al (2009). The subjects were told to “forcefully” swallow on the videoflouroscopy. Is this study measuring the changes from therapy, or just the immediate flouroscopic changes when told to forcefully swallow? Results were noted in two short paragraphs. Basically, the only parameter that changed significantly was vertical elevation of the larynx. This may be due to the effortful swallow alone, as we have seen from previous studies, surface estim cannot really target the thyrohyoid muscle to elevate the larynx. The following biomechanical measurements had no change or were not to statistically significant levels: anterior and vertical hyoid movement, anterior laryngeal movement, and UES opening. I cannot agree with one of the conclusions noted clearly in the abstract: “Effortful swallow training combined with electrical stimulation increased the extent of laryngeal excursion.” When we use the term excursion, we should think about the anterior and superior movement of the hyolaryngeal complex.

2. Sun, S.F., et al (2013) combined neuromuscular electrical stimulation (NMES) with fiberoptic endoscopic evaluation of swallowing (FEES) and traditional swallowing therapy to determine if swallowing function can improve in moderate-severely impaired stroke patients. However, again, the patients were 3+ weeks post-stroke, and no chart available to see the details. Are the results valid indicators of NMES combined with therapy or spontaneous recovery?

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Did DRS2015 shed new light on electrical stimulation?

There was some action at the Dysphagia Research Society annual meeting in March, 2015 regarding electrical stimulation.

1. Takahashi, et al., from Niigata University (2015, March) studied 18 young healthy adults and the effects of neuromuscular electrical stimulation (NMES) when placed on submental surface of the neck. Specifically, they measured the effects on tongue pressure and hyoid elevation. The volunteers swallowed 5 ml liquid 12 times before NMES, during NMES and after NMES. NMES was set at 0.2 ms pulse duration at 80 Hz, with the intensity “set at the level of maximal tolerance in each subject.”

• Tongue pressure was smaller during NMES; however, pressures post-NMES were larger than pre-NMES.
• Hyoid position at rest descended during NMES.
• However, after NMES the hyoid at rest and in maximum elevation was positioned more superiorly than pre-NMES.
• The highest upward-forward position of the hyoid during NMES was lower versus before and after NMES.
• While the overall deflection distance was affected by NMES, the vertical distance was larger during NMES versus pre- and post-NMES.

Maybe in healthy adults, the person compensates for the downward pull and the smaller pressures during NMES. This compensation may rebound to have higher tongue pressures and hyoid elevation after NMES. No long-term effects were mentioned. I look forward to this poster analyzed further in a publication.

2. Estim and patients with Head and Neck Cancer:

I have seen talks in the past from Dr Susan Langmore regarding the 5 year, 16 site, randomized-controlled clinical trial which enrolled 170 head and neck cancer survivors into two arms (Langmore, et al., 2013, March). One group received estim plus swallowing exercises and the other had sham estim and swallowing exercises. Groups were given a home program (with regular clinic visits to ensure accuracy). They performed stretches and 60 swallows paired with real or sham estim. Frequency was 2 times/day, 6 days/week for 12 weeks. The initial analysis of the data at DRS 2013 indicated that estim did NOT enhance swallowing exercises.

Gintas Krisciunas, from Langmore’s team, presented at this year’s Dysphagia Research Society Annual Meeting (2015, March) on the impact of the subjects’ compliance with the home program. Compliance was defined as performing at least 10-12 sessions per week. Estim continued to not show benefit; in fact, when the patients were MORE compliant with estim, they did even worse. Specifically, “compliant patients in the sham estim group realized significantly better Penetration/Aspiration Scale (PAS) scores than compliant patients in the active estim group.”

The team further concluded that the efficacy of swallowing exercises in this group needs to be questioned. Additionally, do we over or under prescribe swallowing exercises? A standard dose and frequency has yet to be determined.

Langmore’s other session on the impact of time post-radiation on patient outcomes indicated that patients who receive therapy within 6 months post radiation do much better (Langmore, et al., 2015, March). Would earlier intervention at higher frequencies change the outcomes stated above?

3. How about gradually increasing the estim intensity?

Serel, Macrae, Humbert & Vose presented a poster at DRS 2015 (Serel, et al., 2015, March) studying gradual increases in electrical stimulation intensity (perturbations) in healthy adults. As stated in their purpose: “when surface electrical stimulation is abruptly applied to the neck (sudden onset at highest tolerated intensity), peak hyolaryngeal elevation in initially reduced.” This lowering of the hyolaryngeal complex is caused by stimulating the infra-hyoid muscles closer to the surface, and it can open the laryngeal vestibule, resulting in aspiration. However, they also noted that Humbert, et al (2013) found that there is error-based learning, as healthy adults are gradually able to increase the elevation back to their baseline heights. Per this poster, they did find that gradual increases in stimulation intensity across the 10 trials reduced the drastic effects. “During the perturbation, gradually increasing stimulation levels lead to a gradual decrease in the duration to max hyoid elevation and to laryngeal vestibule closure onset.” The subjects were able to overcome the negative effects of the stimulation and return to pre-perturbation levels over several trials.

See further discussion of error-based learning in Humbert, et al’s article in AJSLP (2015, February).

4. Can’t we just stimulate inside the pharynx to avoid these issues with surface stimulation? Why not? New Horizons is out in the Kuiper Belt beyond Pluto. So let’s think outside the box too.

What about direct pharyngeal stimulation?

This is called Electrical Pharyngeal Stimulation (EPS). A catheter is placed in the pharynx (15-16 cm from the nostril) that is ringed with electrodes.

A quick search on PubMed will bring up volumes of work particularly by Hamdy, S, Michou, E, and others, from the University of Manchester, UK, regarding inducing neuroplasticity in the neuronal swallowing with EPS in patients post-CVA.

Sonja Suntrup presented on behalf of her team from the University of Muenster, Germany at DRS, and they won the New Investigators Award (Suntrup, et al., 2015, March). They described how the “stimulation was delivered via a pair of bipolar ring electrodes mounted on an intraluminal catheter positioned in the pharynx.” They measured blood and saliva samples to evaluate if electrical pharyngeal stimulation (EPS) can increase the pharyngeal concentration of Substance P.

But, what is Substance P??

Substance P is a neuropeptide that is released by the pharyngeal mucosa. It is known to enhance the cough and swallow reflex (Suntrup, et al., 2015, March). Substance P levels have been found to be reduced after stroke and may contribute to dysphagia.

Suntrup, et al (2015, March) found that 10 minutes of real EPS (versus the sham EPS) immediately increased the level of Substance P in the saliva by 29%. However, the effect was shortlasting and gone after 5 minutes. The investigators question if repetitive treatments with EPS post-CVA could have potential in dysphagia rehabilitation. This needs further research and is not clinic-ready yet.

Summary:

I hope my honest exploration into my own history with electrical stimulation helps foster further respectful discussion. I realize I may have looked at research articles through my own clouded lens. I do strive for a “critical thinking” lens, as Dr Humbert recommends.

Please share articles that you have analyzed, as this blog is by no means an exhaustive systematic review. I hope this prompts guest bloggers, relating different points of view and experience. I realize there are many personal success stories associated with this treatment modality.

Data from the New Horizons Pluto fly-by will take 16 months just to download! Then, scientists (like my son?) may spend the next 20 years combing through that data!

Similarly, there have been some positive findings on electrical stimulation, but more research is needed. Is it truly clinic-ready? I cannot answer that definitively. It seems there may be certain patients who can benefit greatly.

I want to sincerely thank Dr Humbert for her assistance with this blog! Her final thoughts regarding the dilemma of long-term treatment studies are with the issue of comparing a control group (standard care only) to an experimental group (electrical stimulation + standard care). “We don’t really know what standard care is, yet it is assumed that standard care is standard (or equal) between the groups.” Is standard care diet modification, compensatory strategies, maneuvers, strengthening exercises, or a combination of all of these? When adding estim to the mix, how do we separate out if the differences were related specifically to the electrical stimulation modality versus due to the subtle differences with the standard care?

I want to also thank our transdisciplinary dysphagia researchers in advance for all the time needed in the lab to discover the physiological and neurological effects of electrical stimulation on swallowing.

May we go forward with open minds.

What you can do now?

1. Use the comment section below to ask Dr Humbert a question. I’ll pass it on!

2. The FREE Live Chat with Dr Humbert is over, but you can listen Dysphagia Grand Rounds #3 about Electrical Stimulation at https://www.dysphagiagrandrounds.com.

Financial and Non-Financial Disclosures: Nothing to disclose, except for membership to the Dysphagia Research Society and the NFOSD. I am not receiving compensation for advertising the prior free chat or the Dysphagia Grand Rounds.

References not already cited in the text above:

Freed, M.L., Freed, L., Chatburn, R.L. & Christian, M. (2001). Electrical stimulation for swallowing disorders caused by stroke. Respiratory Care, 46 (5), 466–474. https://www.ncbi.nlm.nih.gov/pubmed/11309186?access_num=11309186&link_type=MED&dopt=Abstract

Humbert, I.A., Poletto, C.J., Saxon, K.G., Kearney, P.R., Crujido, L., Wright-Harp, W., Payne, J., Jeffries, N. Sonies, B.C. & Ludlow, C.L. (2006). The Effect of Surface Electrical Stimulation on Hyo-laryngeal Movement in Normal Individuals at Rest and During Swallowing. Journal of Applied Physiology, 101 (6), 1657-1663. doi:  10.1152/japplphysiol.00348.2006 https://jap.physiology.org/content/101/6/1657

Humbert, I.A., Christopherson, H. & Lokhande, A. (2015, February). Surface electrical stimulation perturbation context determines the presence of error reduction in swallowing hyolaryngeal kinematics. American Journal of Speech-Language Pathology, 24, 72-80.

Krisciunas, G.P., McCulloch, T., Lazarus, C.L., Pauloski, B.R., Meyer, T.K., Graner, D., Van Daele, D., Silbergleit, A.K., Crujido, L.R., Kotz, T., Castellano, K. & Langmore, S.E. (2015, March). Impact of Compliance on Dysphagia Rehabilitation Outcomes: Results from a Multi-Center Clinical Trial Evaluation the Efficacy of Electrical Stimulation for Dysphagia. Paper presented at the Dysphagia Research Society 23^rd Annual Meeting, Chicago, IL.

Langmore, S.E., McCulloch, T., Logemann, J., Lazarus, C. & Krisciunas, G. (2013, March). Efficacy of Electrical Stimulation and Exercise in Patients with Dysphagia after HNC: A RCT (2007-2012). Paper presented at Dysphagia Research Society 21^st Annual Meeting, Seattle, WA.

Langmore, S.E., Krisciunas, G.P., Lazarus, C.L., McCulloch, T. Pauloski, B.R., Van Daele, D.J., et al. (2015, March). The Impact of Time Post-Radiation on Dysphagia in HNC Patients Enrolled in a Swallow Therapy Program. Paper presented at the Dysphagia Research Society 23^rd Annual Meeting, Chicago, IL.

Leelamanit, V., Limsakul, C., Geater, A. (2002). Synchronized electrical stimulation in treating pharyngeal dysphagia. Laryngoscope, 112, 2204–10. doi:10.1097/00005537-200212000-00015.

Ludlow, C.L., Humbert, I., Saxon, K.G., Poletto, C.J., Sonies B.C. & Crujido L. (2007). Effects of surface electrical stimulation both at rest and during swallowing in chronic pharyngeal dysphagia. Dysphagia, 22 (1), 1-10. doi: 10.1007/s00455-006-9029-4

Park, J.W., Oh, J.C., Lee, H.J., Park, S.J., Yoon, T.S. & Kwon, B.S. (2009). Effortful swallowing training coupled with electrical stimulation leads to an increase in hyoid elevation during swallowing. Dysphagia, 24, 296-301. doi: 10.1007/s00455-008-9205-9

Park, J.W., Kim, Y., Oh, J.C. & Lee, H.J. (2012). Effortful swallowing training combined with electrical stimulation in post-stroke dysphagia: A randomized controlled study. Dysphagia, 27, 521-527. doi: 10.1007/s00455-012-9403-3

Serel, S., Macrae, P., Humbert, I. & Vose, A. (2015, March). Gradually Increasing Electrical Stimulation Intensity Improves Timing of Hyo-Laryngeal Kinematics over Several Trials. Poster #40 presented at the Dysphagia Research Society 23^rd Annual Meeting, Chicago, IL.

Suntrup, S., Bittner, S., Recker, S., Meuth, S., Warnecke, T. & Dziewas, R. (2015, March). Electrical Pharyngeal Stimulation Increases Substance P Level in Saliva. Paper presented at the Dysphagia Research Society 23^rd Annual Meeting, Chicago, IL.

Takahashi, K., Hori, K., Hayashi, H., Fujiu-Kurachi, M., Ono T. & Inoue, M. (2015, March). Impact of Submental Neuromuscular Electrical Stimulation on Tongue Pressure and Hyoid Movement. Poster #103 presented at the Dysphagia Research Society 23^rd Annual Meeting, Chicago, IL.

Wijting, Y. & Freed, M.L. (2003) VitalStim Therapy Training Manual. Hixson, TN: Chattanooga Group.